1. Field of the Invention
This invention relates generally to ground proximity warning systems, and to systems that modulate the warning envelope of the system in accordance with various parameters to reduce nuisance warnings without sacrificing sensitivity. In particular, the system according to the invention relates to modulating a below glide slope alerting envelope to permit the aircraft to fly below the glide slope under flight conditions where the aircraft is not descending too steeply, for example, during level or climbing flight conditions and even certain shallow descents. Alternatively, the repetition rate of the glide slope alert may be varied to reduce the frequency of the alert during level or ascending flight to provide the pilot an indication of the urgency of the alert.
2. Description of the Prior Art
A system that modulates an excessive descent rate envelope as a function of glide slope deviation is disclosed in U.S. patent application Ser. No. 07/666,094, filed on Mar. 7, 1991; however, the above-mentioned application does not disclose the modulation of a below glide slope warning envelope as a function of flight path of the aircraft as is contemplated by the present invention.
Systems that vary the repetition rate of an alert or a warning are also known. For example, a system disclosed in U.S. Pat. No. 3,925,751 discloses a variable rate advisory warning generator that varies the rate of the advisory warning as a function of the deviation of the aircraft below the glide slope, with the repetition rate being increased as the deviation below the glide slope increases. However, there is no suggestion of varying the repetition rate of the below glide slope alert as a function of the flight path of the aircraft.